• Cornea/External Disease

    Review of: Biomarkers of in vivo limbal stem cell function

    Le Q, Chauhan T, Cordova D, et al. The Ocular Surface, January 2022

    Cellular changes in the cornea and limbus in limbal stem cell deficiency (LSCD) can be quantified utilizing in vivo laser scanning confocal microscopy (IVCM) and anterior segment optical coherence tomography (AS-OCT). Clinical presentation using slit-lamp biomicroscopy, in combination with IVCM and AS-OCT imaging modalities, were used to increase accuracy in detection and staging of LSCD.

    Study design

    A total of 126 subjects (172 eyes) with LSCD and 67 control subjects (99 eyes) without LSCD were included for this observational cross-sectional comparative study. The etiologies of the cases of LSCD enrolled (in order of most to least common) were: iatrogenic injury, contact lens wear, chronic cicatricial ocular surface inflammation, chemical injury, idiopathic cause, aniridia, and neurotrophic keratopathy. Patients were examined with slit-lamp biomicroscopy, IVCM, and AS-OCT to determine cutoffs and correlations for clinical score, cell morphology score, basal cell density (BCD), central corneal epithelial thickness (CET), limbal epithelial thickness (LET), total corneal nerve fiber length (CNFL), corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), and tortuosity coefficient.

    Outcomes

    The clinical score was negatively correlated with a decrease in central cornea BCD, limbal BCD, CET, mean LET, maximum LET, CNFL, CNFD, CNBD, and tortuosity coefficient. Correlations were strongest with BCD, CET, and CNFL in the central cornea. Receiver operating characteristic (ROC) curves of these 3 variables were generated, and the following thresholds were determined: 7981 cells/mm2 for BCD, 51 μm for CET, and 10,448 μm/mm2 for CNFL. Tertiles were established to grade LSCD severity, and a weighted scoring formula for diagnosis was developed.

    Limitations

    Incorporating cell morphology grading was excluded from the final LSCD scoring system because of the challenge of intraobserver variability/subjectivity. This diagnostic methodology also requires multiple expensive in vivo imaging systems, clinical laboratory capabilities for processing immunocytologic specimens, and highly trained personnel, which would limit the method to exclusive use in high-resource tertiary care centers.

    Clinical significance

    Diagnosis of LSCD has previously been based on medical history and clinical signs, with impression cytology used as the gold standard diagnostic method. However, these methods are limited in diagnosing severity and may not be sufficient in accurately diagnosing the disease. Morphologic changes of epithelial cells that precede the clinical signs of LSCD can be quantified into representative in vivo biomarkers using multi-imaging modalities. The translation of quantifying these in vivo biomarkers into a grading system can provide a more comprehensive assessment of the presence and severity of LSCD, thus reducing bias caused by reliance on a single parameter.